In the petroleum industry, especially in conjunction with well production and pipeline transportation of petroleum products, the most widely used valves are gate valves. Typically, gate valves fall into two basic categories, i.e. those valves incorporating slab-type gates and valves having expanding gates. In many cases, it is desirable to provide means for enhancing the sealing ability of a valve through utilization of some motive force. In some cases, the pressure of the fluid controlled by the valve can be used for seal enhancement. In the case of slab-type gate valves, the seat assemblies may be energized by the pressure of the fluid medium controlled by the valve. In other cases, enhancement of the sealing ability of a valve may take the form of hydraulic or pneumatic actuating means or any one of a number of suitable mechanisms for mechanically increasing the engagement force between the seats and the gate structure of a valve mechanism.
Expanding type gate mechanisms have been widely used in the petroleum industry in both wellhead and pipeline valves. In some cases problems develop because of the inability of an expanding gate mechanism to remain centralized during movement between the open and closed positions thereof. The high pressure to which these valves may be subjected causes the downstream segment of the expanding gate mechanism to float or be urged downstream where pressure induced sealing is accomplished between the downstream gate segment and the downstream seal. Movement of the gate under these conditions can develop excessive friction that might cause excessive erosion or galling of the gate or seats during operation. It is desirable to provide means for centralizing the gate mechanism during operation.
In many cases it is desirable to provide means for retaining valve seats within a valve body and to insure ease of removing the valve seats for repair or replacement. In many cases the valve seats can become corroded and eroded to the point that the valve body structure itself may be severely damaged by seat removal.
A most desirable feature in gate valves is the desirability of providing a valve structure that minimizes pressure drop as fluid flows through the valve. Where the flow passage extending through the valve body, valve seats and gate assembly remains of substantially identical diameter, the valve may be referred to as a through conduit type gate valve having essentially the same pressure drop as an equal length of identical diameter pipe. It is important when utilizing an expanding type gate system that the attributes of through conduit type gate valves be maintained.
In many cases it may be desirable to replace or repair valve stem thrust bearings and packing systems without shutting down the flow line controlled by the valve. Back-face seating type sealing systems have been developed and utilized in the past for establishing a seal between the bonnet structure of the valve and the valve stem. Since metal-to-metal type seals are difficult to establish and maintain, it is desirable to provide a back-face sealing system having means for insuring seal integrity and reliability so that such repair operations can be carried out without any sacrifice from the standpoint of safety.
It is a feature of the present invention to provide a novel expanding gate valve system incorporating an expanding gate that is capable of expanding at both the open and closed positions thereof to enhance sealing ability of the valve mechanism.
It is another feature of the present invention to provide a novel expanding gate valve mechanism incorporating an expanding gate and gate centralizer system that centralizes the position of the gate at all times.
Another important feature of the present invention involves the provision of a novel expanding gate valve mechanism that insures accurate positioning of the gate port relative to the flow passages of the valve, thus insuring optimum fluid handling characteristics.
It is also a feature of the present invention to provide a novel expanding gate valve mechanism that is of the through conduit type, offering no more resistance to flow than an equal length of equal diameter conduit.
Among the several objects of the present invention is noted the contemplation of a novel expanding gate valve mechanism incorporating partially cylindrical seat carrier elements located within a generally cylindrical valve chamber and which support floating seat elements within the valve chamber.
It is also a feature of the present invention to provide a novel expanding gate valve mechanism including seat and seat carrier assemblies that are easily and quickly removable and replaceable.
It is another feature of the present invention to provide a novel expanding gate valve mechanism incorporating a back seat system utilizing the combination sealing ability of a metal-to-metal seat and a deformable seat element to achieve sealing between the bonnet and valve actuator mechanism when desirable for replacement of thrust bearings and packing assembly structure of the valve mechanism.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration of this entire disclosure. The form of the invention, which will now be described in detail, illustrates the general principles of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.